Timothy H. Heaton
Department of Earth Sciences
University of South Dakota
Vermillion, SD 57069
Until recently Ursus arctos was thought never to have inhabited Prince of Wales and to have reached other islands of the Alexander Archipelago only after the Wisconsin glacial. This was surmised from its current distribution and from its late appearance south of the ice sheets. Part of the underlying assumption was that southeast Alaskan islands were overridden by ice and were therefore uninhabitable during the glacial maximum. The theory that bears reached the archipelago from the mainland as or after the Cordilleran glaciers melted can be called the "inland colonization theory" (expounded by David R. Klein).
While the inland theory may be the best explanation for the island distribution of many mammalian taxa, fossil studies on Prince of Wales Island suggest an alternate theory for colonization by bears. Remains of at least 13 post-glacial U. arctos have been recovered from three caves dating from 7,205 +/- 65 to 12,295 +/- 120 years B.P., showing that this species did once inhabit the island. Ursus arctos remains from a fourth cave date to 35,365 +/- 800 years B.P. and are associated with remains of U. americanus. This date is middle Wisconsin and predates the late Wisconsin glacial maximum.
During glacials the Alexanders may have sported habitable coastal refugia with access to marine food, and glacial bridges would have made inter-island travel easier than at present. Arrival of mammals by this hypothetical route to isolated refugia can be called the "coastal colonization theory." Under this theory the island populations are relectual, and the Ice Age promoted rather than inhibited colonization.
The coastal colonization theory provides the simplest explanation for the fossil record of bears on Prince of Wales Island. Stable isotope analysis indicates that the middle Wisconsin U. arctos had more of a marine diet than its postglacial counterparts.